In the context of multimedia design, several kinds of heterogeneous terminals are supposed to be able to receive and recover content provided by the same server.
However, the terminals have different capabilities, in terms of hardware or software functionalities. These terminals can be desktop personal computers, laptop computers, personal digital assistant (PDA), portable phones, or digital television receivers. As it is easily understandable and well known, these terminals cannot read the same content. As a simple example, one can easily understand that these terminals cannot each display a same image with the same resolution.
The MPEG-4 standard (defined in the document ISO/IEC 14496-1:2001 Systems) consortium has defined a number of profiles according to devices that have to be MPEG-4 compliant. The profiles are defined in the document N3932 “New MPEG-4 Profiles Under Consideration”.
For example, some PDAs will be able to play only MPEG-4 compressed audio/video contents and some MPEG-4 compliant computers will be able to play all MPEG-4 profiles.
The problem of MPEG-4 content creators is to design content that is understood by platforms that do not comply with the profile of the received content. A content created for some specific MPEG-4 profiles cannot be displayed on platforms that do not comply with the content's profiles or at least not on those that comply with a profile of a lower level. Moreover, the number of defined profiles is quite important as each profile is also split into different levels, each level defining parameters such as visual resolution or a data rate for instance.
The document “Design of a framework for dynamic content adaptation to web-enabled terminals and enterprise applications” published in the proceedings of the Sixth Asia Pacific Software Engineering Conference pages 72 to 79 concerns a method to adapt content to terminals having different capabilities. A solution that selects, deletes or converts each element of a web document's contents appropriately according to the type of devices is proposed. Despite the fact that the document describes a dynamic adaptation system, the adaptation is carried out at the transmitter, resulting in many different versions of the content to be transmitted.
This solution is not adapted to a system comprising a great number of terminals, where it is desirable to send a same content to the largest possible number of terminals, or a system in which the transmitter has no advance knowledge of parameters stored in a particular terminal.